The subject matter disclosed herein relates to vacuum electrode devices in general, including but not limited to x-ray tubes, electron beam source devices, power electronic devices, such as a klystron, ignitron, and others, and more specifically to devices and procedures for determining the pressure present within the vacuum electrode device.
Vacuum electron devices are used in a variety of systems in order to generate electrons for different purposes. In one example, as shown in FIG. 1 a vacuum electron device is used in an X-ray system 10 in the detection of internal structures of components of an object or item 16 being imaged.
The X-ray system 10 includes an x-ray source 12 configured to project a beam of X-rays 14 through an object 16. Object 16 may include a human subject, pieces of baggage, or other objects desired to be scanned. X-ray source 12 may be a conventional X-ray tube producing X-rays having a spectrum of energies that range, typically, from 30 keV to 200 keV. The X-rays 14 pass through object 16 and, after being attenuated by the object, impinge upon a detector 18. Each detector in detector 18 produces an analog electrical signal that represents the intensity of an impinging X-ray beam, and hence the attenuated beam, as it passes through the object 16.
A processor 20 receives the signals from the detector 18 and generates an image corresponding to the object 16 being scanned. A computer 22 communicates with processor 20 to enable an operator, using operator console 24, to control the scanning parameters and to view the generated image. That is, operator console 24 includes some form of operator interface, such as a keyboard, mouse, voice activated controller, or any other suitable input apparatus that allows an operator to control the x-ray system 10 and view the reconstructed image or other data from computer 22 on a display unit 26. Additionally, console 24 allows an operator to store the generated image in a storage device 28 which may include hard drives, flash memory, compact discs, etc. The operator may also use console 24 to provide commands and instructions to computer 22 for controlling a source controller 30 that provides power and timing signals to x-ray source 12.
In the X-ray source 12, the cathode and anode are disposed within a frame/housing for the X-ray source/tube that is evacuated around the cathode/emitter and the anode in order to remove any gases that would otherwise interfere with the flow of electrons between the cathode and the anode. The housing is desired to enclose a perfect vacuum. However, as a result of imperfections in the materials and processes involved in manufacturing of the housing and the X-ray source 12, an amount of a gas, such as N2, H2, Ar, can be present within the housing. In addition, over time, other imperfections or irregularities in the construction of the housing or internal component outgassing can increase the gases in the housing, further compromising the operation of the vacuum electrode device. The reason for this is that when gas molecules are present in the housing, the electrons produced at the cathode can strike the gas molecules, ionizing the gas molecules and preventing the electron from reaching the anode to produce X-rays. Further, the ionized gas molecules can be drawn towards and strike the emitter/cathode, causing damage to the cathode which results in premature failure of the emitter/cathode and X-ray source 12. As a result, the presence of significant amounts of gas molecules within the housing presents serious negative effects on the longevity and the performance of the X-ray source 12. Thus, it is highly desirable to be able to determine the presence and amount of any gas within the housing in order to maximize the operation of the X-ray source 12.
The presence of a gas within the housing can be determined by measuring the gas pressure within the housing. With prior art vacuum electron devices/X-ray sources 12, in order to test the vacuum electron device for the amount of gas present in the housing, these prior art devices utilize one of two methods: the devices include a stand-alone pressure gauge 100 built into the housing for the X-ray source 12; or the pressure is determined using the emitter/cathode of the vacuum device directly. In either method, the pressure of the gas within the housing is determined by heating a cathode, either in the pressure gauge 100 or the cathode, and creating ionized gas particles that are drawn to a corresponding anode (not shown). The current produced by the ionized gas between the cathode and the anode can then be utilized to determine the gas pressure within the housing.
Issues with these prior art methods and devices include the increased complexity and cost associated with the stand-alone pressure gauge 100 to be attached to the housing and the fact that the vacuum device cathode could potentially be damaged by using it for pressure measurement if the pressure within the housing is high. In the ease of vacuum electrode devices that have been returned for analysis due to poor performance or for testing of the vacuum electron device during manufacture, damaging the cathode is undesirable as it prevents the cathode and other components of the vacuum electrode device from being able to be reused in other devices.
Hence it is desirable to provide a vacuum electrode device such as an X-ray source/tube with a pressure measurement device, system or feature that does not greatly increase the complexity of the device, and that does not need the cathode of the vacuum device in order to determine the pressure within the housing.